1. Technical Field
The present invention relates to a liquid crystal panel, and more particularly to a liquid crystal panel with a wide viewing angle and a high display quality.
2. Description of Related Art
Liquid crystal molecules in a liquid crystal panel do not have an illuminant property. The liquid crystal panel displays color using an electric field to control twist of the liquid crystal molecules to change the light permeability coordinating with a color filter and polarizers. The type of the liquid crystal molecules of a typical liquid crystal panel can be a twist nematic type or a super twist nematic type, and the range of the viewing angle of the liquid crystal panel is narrow. Therefore, an optical compensator may be added to the liquid crystal panel to solve the problem of a narrow viewing angle. Another typical technique is a four-domain vertical alignment technique, which divides each pixel element into four domains by separately disposing a plurality of protrusions and slits on internal surfaces of two substrates facing each other. Liquid crystal molecules in each domain align along four specific directions to obtain a wider viewing angle.
Referring to FIGS. 10 and 11, FIG. 10 illustrates a plane view of a portion of a typical four-domain vertical alignment liquid crystal panel, and FIG. 11 illustrates a cross-sectional view taken along line II-II of FIG. 10. The typical four-domain vertical alignment liquid crystal panel 100 includes a first substrate 110, a second substrate 120 opposite to the first substrate 110, and a liquid crystal layer 130 sealed between the first substrate 110 and the second substrate 120. The liquid crystal 130 is composed of anisotropy liquid crystal molecules 131 with a negative dielectric constant.
The first substrate 110 includes a first base 111, a color filter 113, a common electrode 115, and a plurality of first and second protrusions 117 and 119. The color filter 113, the common electrode 115, and the first and second protrusions 117 and 119 are disposed in sequence from the first base 111 toward the liquid crystal layer 130, and are placed between the first base 111 and the liquid crystal layer 130. The color filter 113 includes a plurality of red color filter elements (not shown), green color filter elements (not shown) and blue color filter elements (not shown), which are arranged periodically.
The second substrate 120 includes a second base 121, a plurality of parallel scan lines 122, a plurality of parallel data lines 124 vertically intersected and isolated with the scan lines 122, a plurality of pixel electrodes 123, and a plurality of first and second slits 125 and 127 formed on the pixel electrodes 123. The scan lines 122, the data lines 124, the pixel electrodes 123, and the first and second slits 125 and 127 are formed on a side of the second base 122 adjacent to the liquid crystal layer 130. The data lines 124 and the scan lines 122 intersect to define a plurality of pixel elements 140. The pixel electrodes 123 correspond to the pixel elements 140. The pixel elements 140 respectively correspond to the red, green or blue color filter elements.
Each pixel element 140 includes two first protrusions 117, a second protrusion 119, two first slits 125 and two second slits 127.
A midline of the pixel element 140 parallel to the scan lines 122 is referred as a symmetry axis 142. The two first protrusions 117 are symmetrical to the symmetry axis 142. Each first protrusion 117 includes a straight bar 117a and a first extension portion 117b. The first extension portion 117b is vertical to the symmetry axis 142 and is located along an edge of the middle region of the pixel element 140. An acute angle is formed between the straight bar 117a and the symmetry axis 142. One end of the straight bar 117a is connected to the first extension portion 117b, and the other end of the straight bar 117a extends to one corner of the pixel element 140.
The second protrusion 119 is located in the middle region of the pixel element 140 and is symmetrical to the symmetry axis 142. The second protrusion 119 includes a V-shaped portion 119a and three second extension portions 119b. Two sides of the V-shaped portion 119a are respectively parallel to the straight bars 117b. One of the second extension portions 119b and the V-shaped portion 119a are combined in a Y shape. The other two of the extension portions 119b are respectively connected to two ends of the V-shaped portion 119a, and are vertical to the symmetry axis 142, i.e. the two second extension portions 119b are parallel to the two first extension portions 117b and are located along another edge of the middle region of the pixel element 140.
The two first slits 125 are symmetrical to the symmetry axis 142, and are located between the two first protrusions 117 and the second protrusion 119. The two first slits 125 are respectively parallel to the straight bars 117a of the two first protrusions 117 and are substantially arranged in a V shape.
The two second slits 127 are symmetrical to the symmetry axis 142, and are in a straight bar shape. The second slits 127 are respectively parallel to the two straight bars 117a and are located on another two corners of the pixel element 140. The two first protrusions 117 separate the two first slits 125 and the two second slits 127.
The pixel element 140 is divided into a plurality of regions according to the alignments of the liquid crystal molecules 131. The two first slits 125 and the two straight bars 117a define a region A and a region C, and the alignments of the liquid crystal molecules 131 in the A region and the C region are symmetrical to each other. The two first slits 125 and the V-shaped portion 119a define a region B and a region D, and the alignments of the liquid crystal molecules 131 in the region B and the region D are symmetrical to each other. The two straight bars 117a and the two second slits 127 define a region B and a region D symmetrical to the symmetry axis 142. The first extension portions 117b and the second extension portions 119b can make the alignments of the liquid crystal molecules 131 on the edge of the pixel element 140 regularly, thereby avoiding generating a defect of dark lines due to irregular alignments of the liquid crystal molecules 131.
According to the aforementioned description, the pixel element 140 is divided into four regions including the regions A, B, C and D by the first protrusions 117, the second protrusion 119, the first slits 125 and the second slits 127. When a voltage is not applied to the liquid crystal panel 100, the long axis of each liquid crystal molecule 131 is arranged along a direction vertical to the substrate 110 and 120 under the effect of alignment films (not shown) on two inner sides of the liquid crystal layer 130.
When the voltage is applied to the common electrode 115 and the pixel electrodes 123, an electric field substantially vertical to the substrates 110 and 120 is generated between the substrate 110 and 120. In the pixel element 140, due to the existence of the first protrusions 117, the second protrusion 119, the first slits 125 and the second slits 127, the electric field directions adjacent to the first protrusions 117, the second protrusion 119, the first slits 125 and the second slits 127 are tilted, so that one end of the long axis of each liquid crystal molecule 131 tilts to the first protrusions 117 or the second protrusion 119, and the other end of the long axis of the liquid crystal molecule 131 tilts toward the first slits 125 or the second slits 127. As a result, the liquid crystal molecules 131 in the four regions A, B, C and D correspondingly have four alignments of different directions as shown in FIG. 11. Simultaneously, all of the liquid crystal molecules 131 in any region have substantially the same alignment. Thus the liquid crystal panel 100 achieves an effect of four-domain vertical alignment displaying.
However, for each of the liquid crystal molecules 131, a refractive index of the long axis is different from that of the short axis, and the alignments of the liquid crystal molecules 131 of the pixel element 140 are merely four directions substantially. Therefore, when viewing an image displayed by the liquid crystal panel 100 from different directions, especially viewing the image in a large viewing angle, the image is still visible. However, because the liquid crystal molecules 131 have the structural limitation and only have four-domain vertical alignments, the liquid crystal panel 100 may have a serious color-fading phenomenon and even have a whitening phenomenon, thus causing the liquid crystal panel 100 to have a poor display quality.